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Index > Main > Two opcodes for push <imm>?

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Plue



Joined: 15 Dec 2005
Posts: 151
Plue
How come these genrates different opcodes?
push dword 0
push 0

I want the short version when possible, but if I don't put dword after all of my pushes then fasm will error out on indirect memory references. Making my compiler check for this and have it sometimes generate "dword" and sometimes not when it always wants to push a dword seems a bit unneccesary. Can I tell fasm to prefer the short version?

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Post 22 Dec 2006, 12:42
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Tomasz Grysztar



Joined: 16 Jun 2003
Posts: 7724
Location: Kraków, Poland
Tomasz Grysztar
Yes, use the PUSHD mnemonic - it defaults to 32-bit while optimizes imm pushes just like the plain PUSH.
Post 22 Dec 2006, 13:23
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Plue



Joined: 15 Dec 2005
Posts: 151
Plue
If I do
Code:
v_s rb 4
pushd [v_s]    

it doesn't work, but with push dword [v_s] it works.
Post 03 Jul 2007, 16:07
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UCM



Joined: 25 Feb 2005
Posts: 285
Location: Canada
UCM
That's because you can't push a byte onto a dword stack; because you defined it as "rb 4". Change it to "rd 1" or "dd ?" and it should work. See the FASM principles (etc blah blah blah) in the Documentation section, Tomasz will surely link it Razz

The reasoning for this is that
Code:
 pushd [v_s]     
tries to push [v_s] straight onto a dword stack - which can't be done
Code:
 push dword [v_s]     
is overriding the byte assignment into a dword, which FASM allows to be pushed onto a dword stack.

Now, remember that
Code:
 pushd dword [v_s]     
is always available for less confusion - but it might also make it more confusing Razz

Hope you understood that. Very Happy

P.S. Please correct me if I'm wrong. I am at a friend's house, so no FASM to test Sad

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Post 04 Jul 2007, 04:40
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